1. Field of the Invention
The present invention relates to a depletion mode semiconductor device and a manufacturing method thereof, and more particularly, to a depletion mode semiconductor device with a trench gate and a manufacturing method thereof.
2. Description of the Prior Art
Generally, transistors include enhancement mode transistors and depletion mode transistors. In the depletion mode transistor, the channel may exist without voltages applied to the gate electrode by modifying the doping concentration in the channel. A negative voltage has to be applied to the gate electrode to close the channel in the depletion mode transistor. Therefore, the depletion mode transistor is a kind of normally-closed transistor, and in contrary, the enhancement mode transistor is a kind of normally-open transistor.
The depletion mode transistor may be constructed by a horizontal structure or by a vertical structure. The electrical capacitance is relatively lower and the operation speed is relatively higher in the depletion mode transistor constructed by the horizontal structure. Higher breakdown voltages and higher integrated density could be realized with the depletion mode transistor constructed by the vertical structure.
As smaller electric devices are continually developed, the distance between each of the devices in the transistor keeps on getting smaller. For instance, in the depletion mode transistor constructed by the vertical structure, the distance between the source electrode and the drain electrode becomes smaller, or the depths of the source electrode and the drain electrode become shallow. The modification approach for reducing the volume of the electric device may lower the resistance of the electric device but also may induce the punch through effect in the depletion mode transistor.